=============================================
-SNOW Video Codec Specification Draft 20070103
+Snow Video Codec Specification Draft 20080110
=============================================
-Intro:
-======
-This Specification describes the snow syntax and semmantics as well as
-how to decode snow.
-The decoding process is precissely described and any compliant decoder
-MUST produce the exactly same output for a spec conformant snow stream.
-For encoding though any process which generates a stream compliant to
-the syntactical and semmantical requirements and which is decodeable by
+Introduction:
+=============
+This specification describes the Snow bitstream syntax and semantics as
+well as the formal Snow decoding process.
+
+The decoding process is described precisely and any compliant decoder
+MUST produce the exact same output for a spec-conformant Snow stream.
+For encoding, though, any process which generates a stream compliant to
+the syntactical and semantic requirements and which is decodable by
the process described in this spec shall be considered a conformant
-snow encoder.
+Snow encoder.
Definitions:
============
qlogs
}
if(!keyframe){
- if(!always_reset)
- update_mc b header_state
- if(always_reset || update_mc){
+ update_mc b header_state
+ if(update_mc){
for(plane=0; plane<2; plane++){
diag_mc b header_state
htaps/2-1 u header_state
|hcoeff[i]| u header_state
}
}
+ update_qlogs b header_state
+ if(update_qlogs){
+ spatial_decomposition_count u header_state
+ qlogs
+ }
}
spatial_decomposition_type s header_state
block(0)
block(level):
+ mvx_diff=mvy_diff=y_diff=cb_diff=cr_diff=0
if(keyframe){
intra=1
- y_diff=cb_diff=cr_diff=0
}else{
if(level!=max_block_depth){
s_context= 2*left->level + 2*top->level + topleft->level + topright->level
residual:
+ residual2(luma)
+ residual2(chroma_cr)
+ residual2(chroma_cb)
+
+residual2:
+ for(level=0; level<spatial_decomposition_count; level++){
+ if(level==0)
+ subband(LL, 0)
+ subband(HL, level)
+ subband(LH, level)
+ subband(HH, level)
+ }
+
+subband:
FIXME
quant_table
quantiztation table
+
+Highlevel bitstream structure:
+=============================
+ --------------------------------------------
+| Header |
+ --------------------------------------------
+| ------------------------------------ |
+| | Block0 | |
+| | split? | |
+| | yes no | |
+| | ......... intra? | |
+| | : Block01 : yes no | |
+| | : Block02 : ....... .......... | |
+| | : Block03 : : y DC : : ref index: | |
+| | : Block04 : : cb DC : : motion x : | |
+| | ......... : cr DC : : motion y : | |
+| | ....... .......... | |
+| ------------------------------------ |
+| ------------------------------------ |
+| | Block1 | |
+| ... |
+ --------------------------------------------
+| ------------ ------------ ------------ |
+|| Y subbands | | Cb subbands| | Cr subbands||
+|| --- --- | | --- --- | | --- --- ||
+|| |LL0||HL0| | | |LL0||HL0| | | |LL0||HL0| ||
+|| --- --- | | --- --- | | --- --- ||
+|| --- --- | | --- --- | | --- --- ||
+|| |LH0||HH0| | | |LH0||HH0| | | |LH0||HH0| ||
+|| --- --- | | --- --- | | --- --- ||
+|| --- --- | | --- --- | | --- --- ||
+|| |HL1||LH1| | | |HL1||LH1| | | |HL1||LH1| ||
+|| --- --- | | --- --- | | --- --- ||
+|| --- --- | | --- --- | | --- --- ||
+|| |HH1||HL2| | | |HH1||HL2| | | |HH1||HL2| ||
+|| ... | | ... | | ... ||
+| ------------ ------------ ------------ |
+ --------------------------------------------
+
+Decoding process:
+=================
+
+ ------------
+ | |
+ | Subbands |
+ ------------ | |
+ | | ------------
+ | Intra DC | |
+ | | LL0 subband prediction
+ ------------ |
+ \ Dequantizaton
+ ------------------- \ |
+| Reference frames | \ IDWT
+| ------- ------- | Motion \ |
+||Frame 0| |Frame 1|| Compensation . OBMC v -------
+| ------- ------- | --------------. \------> + --->|Frame n|-->output
+| ------- ------- | -------
+||Frame 2| |Frame 3||<----------------------------------/
+| ... |
+ -------------------
+
+
Range Coder:
============
+
+Binary Range Coder:
+-------------------
+The implemented range coder is an adapted version based upon "Range encoding:
+an algorithm for removing redundancy from a digitised message." by G. N. N.
+Martin.
+The symbols encoded by the Snow range coder are bits (0|1). The
+associated probabilities are not fix but change depending on the symbol mix
+seen so far.
+
+
+bit seen | new state
+---------+-----------------------------------------------
+ 0 | 256 - state_transition_table[256 - old_state];
+ 1 | state_transition_table[ old_state];
+
+state_transition_table = {
+ 0, 0, 0, 0, 0, 0, 0, 0, 20, 21, 22, 23, 24, 25, 26, 27,
+ 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 37, 38, 39, 40, 41, 42,
+ 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 56, 57,
+ 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73,
+ 74, 75, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88,
+ 89, 90, 91, 92, 93, 94, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103,
+104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 114, 115, 116, 117, 118,
+119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 133,
+134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149,
+150, 151, 152, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164,
+165, 166, 167, 168, 169, 170, 171, 171, 172, 173, 174, 175, 176, 177, 178, 179,
+180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 190, 191, 192, 194, 194,
+195, 196, 197, 198, 199, 200, 201, 202, 202, 204, 205, 206, 207, 208, 209, 209,
+210, 211, 212, 213, 215, 215, 216, 217, 218, 219, 220, 220, 222, 223, 224, 225,
+226, 227, 227, 229, 229, 230, 231, 232, 234, 234, 235, 236, 237, 238, 239, 240,
+241, 242, 243, 244, 245, 246, 247, 248, 248, 0, 0, 0, 0, 0, 0, 0};
+
+FIXME
+
+
+Range Coding of integers:
+-------------------------
FIXME
+
Neighboring Blocks:
===================
left and top are set to the respective blocks unless they are outside of
the used luma and chroma is the sum of the predictor and y_diff, cb_diff, cr_diff
to reverse this in the decoder apply the following:
-block[y][x].dc[0] += block[y][x-1].dc[0];
-block[y][x].dc[1] += block[y][x-1].dc[1];
-block[y][x].dc[2] += block[y][x-1].dc[2];
+block[y][x].dc[0] = block[y][x-1].dc[0] + y_diff;
+block[y][x].dc[1] = block[y][x-1].dc[1] + cb_diff;
+block[y][x].dc[2] = block[y][x-1].dc[2] + cr_diff;
block[*][-1].dc[*]= 128;
the remaining points shall be bilinearly interpolated from the
-up to 4 surrounding halfpel points, again rounding should be to nearest and
-halfway values rounded up
+up to 4 surrounding halfpel and fullpel points, again rounding should be to
+nearest and halfway values rounded up
-compliant snow decoders MUST support 1-1/8 pel luma and 1/2-1/16 pel chroma
+compliant Snow decoders MUST support 1-1/8 pel luma and 1/2-1/16 pel chroma
interpolation at least
| + | + | + | + +1/2
-snows 9/7 Integer filter:
+Snow's 9/7 Integer filter:
1. s[i] -= (3*(s[i-1] + s[i+1]) + 4)>>3; for all even i < w
2. s[i] -= s[i-1] + s[i+1] ; for all odd i < w
3. s[i] += ( s[i-1] + s[i+1] + 4*s[i] + 8)>>4; for all even i < w
=====
Important:
finetune initial contexts
-spatial_decomposition_count per frame?
flip wavelet?
try to use the wavelet transformed predicted image (motion compensated image) as context for coding the residual coefficients
try the MV length as context for coding the residual coefficients
use extradata for stuff which is in the keyframes now?
the MV median predictor is patented IIRC
-change MC so per picture halfpel interpolation can be done and finish the implementation of it
-compare the 6 tap and 8 tap hpel filters (psnr/bitrate and subjective quality)
+implement per picture halfpel interpolation
try different range coder state transition tables for different contexts
Not Important:
+compare the 6 tap and 8 tap hpel filters (psnr/bitrate and subjective quality)
spatial_scalability b vs u (!= 0 breaks syntax anyway so we can add a u later)
projects / ffmpeg / blobdiff